Ultra high frequency oscillator



Aug. 29, 1950 P; H. CRAIGr l 2,520,383

ULTRA HIGH FREQUENCY oscILLAToR Filed oct. 1s, 1944 S Q WAVE I 1K F 8 t[O-Iii*f /Oa GENERATQQ l 1 u, n I

Patented Aug. 29, 1950 oj STA-tes `punita.xH-icm Fnaiicysouts'mn, A

RalmerHr Craig, Gainesville;FlaaassignortosI l Invex, Inc.,.acorporation oflori'da; l

.Application Qctoher 18, 1944, Serial No. 559,215

4 Claims.

This invention relates to an electronic oscillator capable of generatingoscillations of ultrahigh:Lfrequencye` An object of fitheff invention iis to A.deviseaan electronic oscillator in which the frequency of theoscillations is dependent upon the speed of the electrons and is notdetermined by resonance of a circuit.

The invention involves an electron tube-lin. which a concentrated beamof electrons is projected through a series of aligned inductor elementseach fof Whichembodiesa pickup, coil.'` The electron stream isinterrupted or varied periodically so that groups or bunches ofelectrons` pass in succession through saidinductor elements. A voltageimpulse of` yone polarity is generated in each coil by each group,ofelectronsapproaching theinductor, and an impulse of oppositepolarity" isgenerated'as eachA electron group recedes from. theinductor. The pickup coils are connected lin acommon output circuit anda `feedback.connection is provided from the output circuit to controlthephase `relation of'the grouping `or bunchingjof they electrons 'in thestream 'in orderto secureimaxirnum amplitude of the voltagesinducedinithe pickup coils.

My `invention is "illustrated inthe accompanying drawing in which Figurel is a diagrammaticrepresentationof the preferredfcrm of theoscillatorcircuit, the electron` tube being shown-in'- longitudinal crosssection:

Figure 2 is a sectional view ofthe magnetic core of an inductor-elementshowing various dimensions and- `factors controlling the operation oftheoscillator; and

FiguresS and4 are diagrams illustrating the voltages `induced in theinductor elements.

Referring to the drawing, the electronic tube employed inthe oscillatoris diagrammatically represented in Figure 1 and may-consister aninsulating envelope l containing-a suitable cathode 2 mounted in one endthereof andlheated from a suitable source 3. An anode orwplateV P ismounted in front ofthefcathodeland `isprovided with a centralaperture oropening Pa. A control grid G'risl1interposedbetween ithevcath-f ode 2and the plate P which `plateis maintained at a `positivepotential fwithrespectuto cathode 2 by a suitable source 4. Asecond anode` Sais pro.-videdin the oppositeendiof thectube `from-...cathode-2- and maymformtmend wall :oi-:tneltubefas shown `in .Figure 1. or. itumay be separatafrom tained: at.` a positive potential:` `witlr` respect` cto plate flPl byYf-meansy of source k 6. `Interposed fbee `tween .platefP andanode V5 is` la series `of `indim- Itors :embodying :magnetic LringsiTI` arranged in .axial alignment fwithf the IaperturelPmin thefplate Pand `being spaced apart at regular intervals. Each magnetic ring:--may'ibe tormedcf com pressed po'vvderedPermalloy, Mumetal,. or othersuitablexmagneticzmaterial.and carries a pickup coil in; IThese pickupcoils are-eonnected in serial circuit relation in an output circuitwhich supplies a load device 8. An uoscillator 9 of suitable.\-constructi0n is.:connected to `supply a control wave to control grid G,and the oscillator is controlled .or synchronized and properlyphasedwith' respect Lto the oscillations in the output circuitby means of afeedback circuit including a. phase shifting filter I'G of V suitableconstruction. In the example shown inJFigure l', the lilter may be`formedA of two series .condensers 10a and 10b `in opposite-sides of theAfeedback connection and a variable'shunt resistance 10c. The functionof controljgrid 'Gjis to `break `upjthe electron* stream passing throughthe4 inductor `elementsinto groups or bunches ofv electrons, and `for4thispurpose I-prcfer `to use `an oscillator at9 producing-fa square-topwave, although other wave shapesmaybe employed:A Asuitableform ofoscillator Vto bejused` at Swill-be found-in Termans Radio EngineeringI-Iandbook ait pages 970 `and 971.

Operation of Figure 1 `is as'follows: Th'eelectrons emitted from cathode`2 are drawn towards 'the plate P -by source' 4 fand Athe velocity ofthe 4electrons passing through the aperture Pa Awill bedeterminedbythehvoltagerof the plate-=P with `respect to the cathode 2.Suitable focusing coils or `electrodes maybe used to concentrate theelectrons on the aperture -Pa- `if desired. The grid lGr serves tointerruptor vary `thestreamfo electro-ns which passes-.through theaperture-` Pa so that the stream `passing" through fthe-aperture isformed-- of a series- `of `successive 1 groupsror bunches of `electronsAwhich are-projectedvalong the common axis of the inductonrings 1.' If1desired, conventional. electron focusing coils or electrodes may beemployed to concentrate and direct the stream along. the:,axis :of i theinductor elements. As` each electronzgroup or bunch :ap-.- proaches.;and:` passes.l through i each inducton a complete.; cycle of voltage'is;` generated inil the associated` pickup.; coil;'la,;and the duration`of the induced cycle i will be dependentV upon;` the speed at which theelectron bunch isftravelling, Since all of the pickup coils areconnected to a common output circuit; each bunch of electrons willinducen:voltagetcvcleineach .pickup coil it passes from plate P to anode5. In other Since the magnetic circuit of ring 'lis uniform Words, inthe example shown in Figure 1, each in cross-section and is symmetricalabout the axis bunch of electrons will induce ten complete of the ring,Equation 1 may be stated in terms of cycles of voltage in the outputcircuit in passing a, b, :c and y as follows:

from plate P to anode 5, and the separation be- 5 tween the successivecycles of voltage will be VQ-Fj dependent upon the speed at which theelectron H=-22-'J=VQ 2y-2 (3) bunch is travelling and upon the distanceof x 'i'y (x iw) separation between adjacent inductor units. The totalflux induced in the magnetic circuit Accordingly, by properly spacingthe inductor 0f ring 1 now becomes: units and by adjusting the speed ofthe electrons, the frequency of the voltage impressed Imis-u 2+!)y'ia--gimdydx upon the output circuit may be controlled. I b V (x 'i'yWith a given spacing between the inductor units, =[Sinh l x Sinh 1 jTi'buVQ the frequency may be varied by varying the voltl/-a 11H-a I-bage of the source 4 or of the source 6 or of both. z+1, b

In order that the succeeding bunch or group =VQ|:S1nh'1 y asmh"1 23" ofelectrons shall have the proper phase relation z+1) z b to augment thevoltage induced by a given bunch sinh-1 +a+sinh1 E .o f electrons, it isimportant that the groups or Y' f 'f Y s yr y l bunches of electronsshall be released by the grid (4) ,G in a predetermined phase relationwith respect The electromotive force induced in any pickup to theoscillations in the load circuit. For this loop wound around ring 1 willbe:

purpose, a feedback circuit including phase From Equation 5 it will beseen that the inshifter l0 is provided for controlling the phase 35duced voltage varies as the square of the velocity relation of thepulses generated by control genof the approaching charge, and directlywith the erator 9 in timed relation with the oscillations in value ofthe charge, the number of turns o'n a. the load circuit. The properphase relation may pickup coil, the permeability and dimensions of besecured by adjusting the values of the elements the inductor core, andthe instantaneous posiin phase shifter I0 until maximum output is ob- 40tion of the charge along the inductor axis. tained in the load circuit.Upon examining the term within the brackets Since energy will beabsorbed from each elecand designating it as F(), it will be found thattron charge or group as it passes through each as a: is varied, thegeneral shape of this funcinductor element, the speed of the charge willbe tion is shown in Figure 3. This figure also repslowed down, and inorder to compensate for this resents the shape of the inducedelectromotve loss in velocity, the anode 5 is maintained at a force. Asthe charge Q approaches the magnetic positive potential with respect toplate P by ring yfrom the left, the induced E. M. F. Vin the Ameans ofsource 6. Additional accelerator pickup coil increases to a maximum at adefinite anodes (perforated anodes) may be inserted at distance 5cm fromthe center of the magnetic .different points along the series of pickupunits ring, and then reduces in value to zero at the in order tocompensate for the loss in energy, and plane of the ring and thereafterincreases to a these additional anodes would be connected to maximumvalue in the opposite direction at +m.

intermediate points on the source 6. One such and then decreases towardszero as the charge i accelerating anode is shown at 5. continues to theright of the ring along the axis. The wave form of the electromotiveforce which Where Several of the inductors are connected is induced ineach pickup coil may be understood in series and are spaced apart byequal distances, from the following. Referring to Figure 2, if Q theindividual voltage cycles generated in the represents la charge movingat a given velocity different coils are represented by the solid, line Valong the axis of magnetic ring '1, then the curves in Figure 4, and theresultant alternating field H of this moving charge at the point S lo-50 voltage produced by a group of electrons passing cated at a distance1' from QY and at an angle through the four coils is represented bythedot- 0 with respect to V may be determined from the ted line curve inthis figure. following equation: If more than one group of electrons ispassing Y 2 through the series of pickup units at the same H VQ Sme o/T(l) 55 time, the resultant Voltage induced in the circuit In Figure 2the point S has been taken at the Will depend UDCH the TeleiVe SDaCIlg0f the center of the magnetic path of the ring 'I which g'IOllpS- It iSimplienb therefore that the Spachas a cross-section of 2b 2a and a meandiameing 0I phasing 0f the eleCtI'On gIOuDS be propter of 2y. The chargeQ is located at a, distance erly controlled. The groups should bereleased in :1: from the central plane of the ring 'I passing I timedfelation Such that they are Separated by a through the point S The iiuxinduced in the distance equal to the spacing between adjacent ying bythe eld H Wi11 be; units or anyrmultiple of this spacing. The proppfuH'd (2) er phasing Aof the electron groups or bunches is determinedbythe phase shifter lll; The fre- -where u is the permeability of thering. quency of the electron groups, or the numberof groups per secondwhich pass through aperture Pa, may be equal to the frequency of thegenerated voltage in the load circuit, or it may be any sub-multiple ofthis frequency.

The value of the resultant voltage generated in the series of pickupcoils will also be dependent upon the length of each electron group orbunch passing through the series of pickup units. For most eicientoperation the electron groups should have a length equal to half thedistance of separation of adjacent pickup units. Other lengths arepossible, but it is preferred to have the electron groups of a length ofone-half the distance of separation between adjacent pickup units or anodd multiple of this length, The importance of the length of theelectron group will become apparent when it is considered that theapproaching end of the group induces a pulse of one polarity in a giveninductor unit while the receding end of the group induces a pulse ofopposite polarity in the same unit. The length of the individualelectron groups or bunches will be determined by the shape of thecontrol wave applied to the grid G from the source 9.

The length of the inductor element along the electron path is also afactor in the shape of the current pulse generated in the pickup coils.Preferably, the inductor elements have a relatively narrow dimension inthe direction of the electron stream with respect to the length of thepath between the plate P and the anode 5, and the inductor elementsshould not have a width along this path greater than one-half thedistance of separation of adjacent units.

A condenser Il may be connected across the load circuit to form aresonant combination with the pickup coils. This will reduce the effectof the inductance of the pickup coils in the output circuit. If desired,small condensers may be connected in series with the circuit between theinductor elements, or the condensers may be connected in parallel withthe pickup coils. Such condensers may be located either inside of thetube or outside and would serve to tune each coil or a group of coils toa particular frequency. Furthermore, it is not essential that the pickupcoils be connected in serial circuit relation to the output circuit, butthey may be connected in parallel relation to the output circuit.

An amplifier may be inserted in the feedback connection either in frontof or behind the phase shifter IU, or the necessary amplication may beobtained in the control generator 9.

It will be obvious that the details of construction of the oscillatortube may be varied in different ways. For example, instead of formingthe inductor elements of magnetic rings with pickup coils wound thereon,these elements may be formed without magnetic cores and the pickup coilswould surround the path of the electron groups and would be spaced apartin the same manner as the magnetic rings. Also, the pickup elements maybe spaced apart by progressively decreasing distances in order tocompensate for the loss in Velocity of the electron groups as they movefrom the beginning towards the end of the series.

I claim:

1. An electronic oscillator comprising, in combination, a source ofelectrons, means acting on said source and producing a stream ofelectrons therefrom directed along a predetermined path, meansperiodically interrupting said stream to form a succession of electrongroups along said path, a plurality of separate inductor elementsmounted in spaced relation along said path and in inductive relation tosaid electron stream, each of said inductor elements including a coil,and an output circuit including said coils connected therein in seriesrelation.

2. An electronic oscillator comprising in combination, a source ofelectrons, means producing a stream of electrons from said source anddirected along a predetermined path, means periodically interruptingsaid stream to form a succession of electron groups along said path,said groups being of uniform lengths, a plurality of inductor elementsmounted in spaced relation along said path and in inductive relation tosaid electron groups passing along said path, each inductor elementincluding a coil, said inductor elements being spaced apart by distancesof the order of twice the length of an electron group, and an outputcircuit having said coils connected therein in series circuit relation.

3. An electronic oscillator according to claim 1 wherein said inductorelement comprises a magnetic ring surrounding said path, and a pickupcoil wound on said ring.

4. An electronic oscillator comprising in combination, a source ofelectrons, means producing a stream of electrons from said source anddirected along a predetermined path, means periodically interruptingsaid stream to form a succession of electron groups along said path, aplurality of inductor elements mounted in spaced relation along saidpath and in inductive relation to the electron stream, each of saidinductor elements including a coil, an output circuit including saidcoils connected in series relation, and a feedback connection from saidoutput circuit to said interrupting means for controlling the phasing ofsaid interrupting means.

PALMER I-I. CRAIG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Re. 21,739 Llewellyn Mar. 4, 19412,009,457 Sloan July 30, 1935 2,074,478 Linder Mar. 23, 1937 2,197,338Fritz Apr. 16, 1940 2,284,751 Linder June 2, 1942 2,295,680 Mouromtseffet al. Sept. 15, 1942 2,299,792 Bouwers et al l- Oct. 27, 1942 2,300,052Lindenblad Oct. 27, 1942 2,272,605 Hesing Feb. 10, 1942 2,305,883 LittonDec. 22, 1942 2,372,193 Fisk Mar. 27, 1945

